场致发射体的局域功函数研究

实际场致发射体表面不可能绝对光滑,而具有原子尺度的微小凸起会导致发射电流大大增加。基于发射电流主要来自于原子尺度微小凸起的假设,提出了局域半球镜像电荷模型,研究了场致发射功函数的降低,发现微小凸起处场致发射的局域功函数会降低而场增强因子将增大。将它代入Ｆ－Ｎ公式计算了一个典型的单尖Ｓｐｉｎｄｔ阴极的发射电流,所得结果与实验符合。在只考虑Ｎｏｔｔｉｎｇｈａｍ效应的情况下,计算了一些材料Ｓｐｉｎｄｔ型     

Spindt阴极金属颗粒粘附失效分析

Spindt型场发射阴极,在初期老炼过程中容易失效,其表现为发射尖锥和栅极间短路、漏电,或是真空电弧损伤。引起Spindt阴极失效的一个主要原因,分析认为是存在于发射尖锥表面、栅极边缘以及承载尖锥的二氧化硅空腔中的金属颗粒附着。这些金属颗粒,产生于双向沉积制作发射尖锥过程中,它们在牺牲层剥离时脱落,并且没有在随后的纯水清洗过程中得到有效去除。这些金属颗粒的存在,即便没有导致初期阴极失效,也可能成为阴极大电流应用,如微波真空功率器件应用的潜在障碍。研究中提出了在常规清洗工艺中引入超声波清洗和兆声波清洗,初步试验研究表明,振动频率28 k Hz的超声波清洗,容易造成阴极损伤,并且对微小颗粒的去除效果不好,而频率1 MHz的兆声波清洗,则可近似无损地将阴极失效率大幅降低。     

场致发射电子源的应用及其研究进展

由于具有低温、电子瞬间发射等优势,场致发射电子源在X射线管、负氢离子源、显示器件等领域都具有应用潜力。本文首先介绍了场致发射的几种应用;比较分析了不同场致发射电子源及其特点;最后结合实验研究工作,分析了类金刚石膜作为场致发射阴极材料的可行性。分析可知:Spindt加工困难且易于损坏;碳纳米管以其独特的结构成为目前研究最热的材料;类金刚石膜易于合成、成份可调节,它兼具的金刚石和石墨的优点使其成为一种潜在的理想场致发射阴极材料。     

常开型后栅极场致发射显示板工作特性的研究

常开型后栅极场致发射显示板是一种新型的场致发射器件.它直接利用阳极使阴极产生场致电子发射,而通过埋在阴极之下的栅极上施加负电压来阻止阴极产生场致电子发射来调制显示所需的图像.为了研究该场致发射显示板的阴极发射特性,本文采用有限元法对场致发射区域内的电场分布进行了模拟计算,用Fowler-Nordheim(F-N)公式计算了阴极表面的发射情况.并研究了阳极电压、阴极电压、阴调距、阴极宽度和阴极厚度等参数的改变对阴极发射特性和栅极调制能力的影响.计算结果显示阴极发射特性和栅极调制能力与上述电参数和结构参数关系密切,从而为优化设计这种显示器件提供了方向.     

碳纳米管冷阴极大电流发射机理的研究

本文对碳纳米管冷阴极的场致发射机理进行了理论和实验研究.研究发现,如果场致发射冷阴极的发射面积很小,有可能得到较大的发射电流密度.当发射面积增加时,冷阴极的平均发射电流密度迅速下降,很难得到大的束电流.研究表明,在碳纳米管冷阴极的场致发射现象中,边沿场的场致发射现象起着非常重要作用.如果仅仅增加发射面积,边沿发射电流增加不多,这导致了平均发射电流密度的下降.因此,在阴极结构中增加发射体的边沿,则可有效提高阴极的发射电流.     

真空二极管阴极表面场致发射模型的研究

为研究真空二极管阴极表面场致发射模型的算法及数值模拟参数对场致发射过程的影响,建立了计算阴极表面电场强度的有限差分近似模型和高斯定理模型,并基于高斯定理模型自行编程对不同间隙距离的二极管进行模拟计算。模拟得到了场致发射过程中阴极表面电场随时间的演变特性及阴极表面稳态电场与外加电场之间的关系,还将阴极表面稳态电场的模拟结果与理论分析结果进行了对比。研究结果表明,空间网格划分数目的多寡对基于高斯定理场致发射模型计算得到的阴极表面电场的影响不大;每个宏电子包含真实电子的数目、二极管间隙距离、二极管外加电场强度等参数均会对数值模拟结果产生显著影响。     

功函数对场致发射稳定性的影响

从理论和实验上研究了材料功函数对场致发射稳定性的影响。研究发现，功函数是决定材料发射稳定性的主要因素。所得数据表明：（1）尖端功函数越稳定，发射电流波动性就越小；（2）尖端的功函数越小，发射的电流也越稳定，强度也越大，所需要的门极电压越低。这一结论在实验研究中充分地得到证实。实验表明，不需要超高真空条件，经过金膜或铯膜覆盖的钽尖端都有稳定的场发射。     

无氧铜基金刚石薄膜场致发射特性研究

采用微波等离子体方法在铜片上沉积了多晶金刚石薄膜，用该薄膜制成的场致发射体的开启电压较低，发射电流密度较高。利用自制的场致发射阵列阴极高真空测试台测试了1-100mA/cm^2的发射电流密度特性，对应的电场强度为2.0-3.5MV/m。从拟合F-N公式得到的功函数φ≈0.025eV,所发射电子轰击荧光屏后能产生明亮的光斑。     

金刚石薄膜阴极电子发射特性研究

宽带隙半导体材料金刚石的负电子亲合势特性使其在电子场发射应用方面备受瞩目。材料的功函数对其热电子发射或场电子发射都有决定性的影响。本文从热电子发射的角度出发 ,对钨基金刚石薄膜阴极有效功函数进行了测量。文章阐述了实验方法、装置及结果 ,测得金刚石涂层阴极的有效功函数为 0 70eV ,并对实验结果进行了理论分析     

场致发射阴极材料的研究与进展

场致发射显示器是一种新型的具有竞争力的平板显示器,场致发射阴极是场致发射显示器的重要组成部分.介绍了各种场致发射阴极材料及其特性,分析了场致发射机理及各种场致发射阴极材料最新进展,并简单讨论了场致发射材料国内外开发应用研究现状及差距.     

石墨烯含量对碳纳米管电极发射器结构和运行稳定性的影响

利用石墨烯电学特性与碳纳米管场发射特性,加入不同含量的石墨烯浆料并对比了各试样场发射特性与器件运行稳定性.实验测试研究结果表明:石墨烯对碳纳米管实现了良好的分隔作用,形成了更大的碳纳米管间隙,降低了电场屏蔽的程度.碳纳米管周围被石墨烯紧密填充,起到了良好的固定作用,能够使碳纳米管获得多级场发射效应.随着石墨烯加入量由2...     

Field electron emitter based on a cesium-gold compound film

The formation and transformation of local emission centers during field electron emission from a cesium-gold (CsAu) compound film on a tungsten point emitter has been studied. Stable electron emission from one center reaches a current density of ～10⁸ A/cm². The properties of emission centers change during the take-off of large electron currents and on heating of the emitter. The experimental data are interpreted assuming that the CsAu compound is decomposed by a narrow beam of current passing through the film, with the formation of a several-nanometer-thick gold column and the reverse process of CsAu compound recovery at the column boundaries due to the diffusion supply of cesium.     

Electron emission properties of CNT arrays grown with micro-molding in capillary (MIMIC) assisted process

We have selectively fabricated carbon nanotubes (CNTs) emitter arrays with a micro mold in capillary (MIMIC) assisted process. The electron emitter growth site was fabricated by resist patterning using the MIMIC process. The pattern was uniformly transferred to the substrate and well aligned CNTs were grown. The emitter produces a turn-on field of 2.7 V/μm with a field emission current of 10 μA/cm². The electron emission current can be controlled by emitter pattern width and pitch variation.     

Fabrication and characterization of a 3D-structured field emitter using carbon nanotube

Carbon nanotube has good electrical properties and a high aspect ratio, which enable it to obtain a high current at a low voltage due to its high field. Due to the life and uniformity of their emission tips, carbon nanotube field emitters are hard to commercialize. A field emitter with a three-dimensional (3D) structure was fabricated in this study to overcome such problems. In the 3D-structured field emitter, the field emission tips are located only at the vertical plane, where an enlarged field emission area can be attained. To fabricate the tip of the 3D-structured field emitter, carbon nanotube/silver nanocomposite powders were fabricated via molecular-level mixing and were sprayed at a substrate with good attachment and homogeneous dispersion between the CNT tips and the silver. The field emission properties of the 3D-structured field emitter were then determined and compared with those of a flat field emitter. The field emission area of the 3D-structured field emitter was found to be 4.5 times larger than that of the flat field emitter, with six times higher current density. Moreover, the 3D-structured field emitter had better stability than the flat field emitter. At a high gate field, the emission images of the 3D-structured field emitter showed light spots expanded towards the gate direction.     

星型阴极的温度分布研究

通过对星型阴极的稳定导热问题进行分析 ,推导出阴极交叉点附近温度分布的近似解析式。并用有限差分数值计算方法对钨基底金属的温度分布进行了计算、分析。数值计算结果和解析结果在常用的阴极温度使用范围内吻合良好 ,表明该解析式在热、热 场、Schottky发射阴极的研究和实际应用中具有实用价值     

Field emission microscopy of graphene on iridium point emitter

The field electron emission from the surface of an iridium point emitter covered by a monolayer graphene film has been studied. An analysis of the field emission images showed that electron emission takes place at the boundaries between graphene islands with dimensions up to several dozen nanometers. Intercalation of alkali metal (cesium) atoms under the graphene film decreases the work function of the emitter but does not change the image. Field ion desorption images obtained in the fields where the surface diffusion of Cs atoms is impossible reveal the presence of a submonolayer concentration of cesium at the defects representing graphene island contacts.     

表面态对碳纳米管场发射的影响

采用CVD法在Ni丝上直接沉积碳纳米管,并应用二极管结构测试表面态(突出尖端和吸附)对碳纳米管场发射的影响。测试表明,突出尖端主要影响碳纳米管场发射的开启电场以及场发射电流稳定性;吸附作用的影响表现在改变碳纳米管能带结构进而改变其场发射性能。     

Emitter spacing effects on field emission properties of laser-treated single-walled carbon nanotube buckypapers

Carbon nanotube (CNT) emitters on buckypaper were activated by laser treatment and their field emission properties were investigated. The pristine buckypapers and CNT emitters' height, diameter, and spacing were characterized through optical analysis. The emitter spacing directly impacted the emission results when the laser power and treatment times were fixed. The increasing emitter density increased the enhanced field emission current and luminance. However, a continuous and excessive increase of emitter density with spacing reduction generated the screening effect. As a result, the extended screening effect from the smaller spacing eventually crippled the field emission effectiveness. Luminance intensity and uniformity of field emission suggest that the highly effective buckypaper will have a density of 2500 emission spots cm(-2), which presents an effective field enhancement factor of 3721 and a moderated screening effect of 0.005. Proper laser treatment is an effective post-treatment process for optimizing field emission, luminance, and durability performance for buckypaper cold cathodes.     

Features of Field Desorption of Sodium and Cesium from the Surface of a Carbonized Rhenium Field Emitter

Technical Physics Letters - We used field emission microscopy to study the field desorption of sodium and cesium atoms from a rhenium field emitter precarbonized in benzene vapor. The dependences...     

Field emission and photo-catalytic investigations on hierarchical nanostructures of copper doped CdS synthesized by kitchen-chemistry approach

We herein report an economical and facile technique for the synthesis of hierarchical nanostructures of Cu doped CdS nanostructures by microwave assisted solvothermal technique using a household microwave oven. We attempted to establish the effect of variation of solvents ratio on the morphological and optical properties of the obtained nanoscale structures. The field emission characteristics of the copper doped CdS nanoarchitecture have been studied and the turn on field is found to be 2.8 V/microm for an emission current density of approximately 0.1 microA/cm2. Emission current stability is determined at the preset current of approximately 1 microA and approximately 10 microA for the stable duration of approximately 4 hrs. The observed field emission results envisage the possibility of using the present emitter in the field emission sources. We believe that this is a unique report on the synthesis as well as field emission studies of copper doped CdS nanostructures. Photocatalytic dye degradation ability of the Cu doped CdS nanostructures is observed to be less than the undoped CdS counterparts.